The correlation measuring methods and devices for measurements of total and fractional immiscible media flow rates based on correlation measuring methods permit measurements of fluid media flow rates without blocking up a pipeline and without affecting its tightness. Therefore they are most preferable solutions for measurements of inflammable and highly explosive media.
The correlation flow rate measuring methods are based on the determination of the maximum value of the correlation function in the course of measuring flow fluctuations over two control cross-sections.
The correlation method for measurements of total and fractional immiscible multiphase media flow rates which was embodied in the device described in patent # 2194950, G01F 1/74, 1/712, G01N 22/04, 20 Dec. 2002 (issued in the Russian Federation) most closely resembles the claimed invention in terms of combined essential features. The known method comprises:                identification of two control sections that are located on a pipeline at a fixed distance from each other;        measurements of fluctuations of the flow dielectric characteristics in each control section with scanning of the flow by the rotating high-frequency electric field;        processing scanning signal with identification of the area with the maximum gain-phase frequency or amplitude-frequency characteristics of the signal;        recording the time of the flow transportation at the peak of the scanning signals' correlation function and determination of fractional composition of immiscible multiphase-media and total and fractional flow rates.        
The known method permits the determination of the total flow rate and fractional composition of two immiscible media if dielectric characteristics of transported media drastically differ from each other. In particular, it is possible to determine water cut in the oil stream when evaluating the well production rate. However, if transported medium comprises gas as well, the measurement of gas volume fraction (GVF) is impossible. The known method does not either permit finding the presence of solid sediments on the pipeline walls, i.e. the presence of paraffin on the walls of the oil pipeline.
There is also a known device for measurements of electroconductive two-phase media flow rate. Said device incorporates a measuring section with an AC magnetic system that has a magneto with two induction coils mounted on two opposite sides of the pipeline, two electrodes on the opposite walls of the pipeline and a control unit which comprises a unit for calculating the correlation function (ref. Inventor's Certificate # 901829, G01F 1/72, G01F 1/74, 30 Jan. 1982 issued in the USSR). The use of the magnetic field ensures a high level of the signal which significantly surpasses interferences, but said device can be used only for measurements of electrically conducting fluids. The performance of said device is good when measuring two-phase media, but it fails to identify fractions of each phase when their number increases.
There is also a known device for measurements of total and fractional flow rates of multiphase immiscible media that comprises a measuring section with two systems on the pipeline walls for scanning a pipeline by the high-frequency electromagnetic field on two different frequencies. Analyzing the received signals, it is possible to calculate the changes of complex dielectric characteristics of the medium (actual and imaginary parts of the complex dielectric constant), and thus to determine phases ratio in the flow (U.S. Pat. No. 4,902,961, NKI 324/640, 20 Feb. 1990). Said device provides a quite accurate determination of phases ratio of multiphase flows, including multiphase flows with dielectric fluids, although it cannot be used to determine fluid flow rate which would require an additional device.
The device described in patent # 2194950, G01F 1/74, 1/712, G01N 22/04, 20 Dec. 2002 issued in the Russian Federation most closely resembles the claimed invention in terms of combined essential features. The known device comprises:                two measuring sections placed along a pipeline, each section equipped with a measuring unit for measurements of fluctuations of flow dielectric characteristics;        high-frequency generator of scanning signals coupled to said measuring units;        the first and the second units for measurements of gain-phase frequency or amplitude-frequency characteristics;        a unit for calculating the correlation function and control microprocessor.Each unit for measurements of fluctuations of dielectric field characteristics is coupled via its own first and second unit for measurements of gain-phase frequency or amplitude-frequency characteristics to a unit for calculating the correlation function. The performance of said device is wholly satisfactory when measuring total and fractional flow rates of immiscible two-phase fluids, including dielectric liquids. Said device is successfully used to determine water cut in the oil stream. However, with water fraction being an exception, said device fails to identify other phases when the number of phases increases, which limits its capabilities.        